Paper - Prenatal growth of the pig
Embryology - 5 May 2024    Expand to Translate
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Lowrey LG. Prenatal growth of the pig (1911) Amer. J Anat. 12(2): 107-138.
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Prenatal Growth Of The Pig
Lawson G. Lowrey
Professor Of Anatomy In The University Of Utah
From The Anatomical Laboratory Of The University Of Missouri
Five Figures
Introduction
Numerous observations on various phases of growth are to be found in the biological literature. Most of those concerning prenatal growth are upon the human embryo, although scattered observations are also recorded on other mammals, and a few on the lower vertebrates. The work presented in this paper was done in the attempt to trace, in the pig, the course of the prenatal growth of the body and especially the relative growth of the various organs. The results are also compared with the course of growth in the human species and in the lower vertebrates, so far as data are available, The work was done in the Anatomical Laboratory of the University of Missouri, under the direction of Dr. C. M. Jackson, to whom I am deeply indebted for his interest, aid and valuable suggestions.
Material and Methods
The material used for this paper consists of 22 litters of pig embryos, comprising about 130 individuals, of which number 105 were used. In most cases, all the pigs of the litter were used, in the others, three or four specimens about the average of the litter were studied. These litters of embryos were secured from the packing houses in Chicago (August 31, 1909), Kansas City (December 27, 1909), and Columbia (at various times, spring 1910). Wherever possible, the litters were worked up in a fresh condition. In the other cases, they were preserved in a 5 per cent aqueous solution of formalin for varying lengths of time (table 1).
For the ovum, some fifty adult ovaries were examined fresh, by opening the large follicles under a dissecting microscope. The ovum (including zona pellucida) was measured with an eye-piece micrometer, whose divisions had a known value. The largest ovum found is considered nearly, if not quite, the size of the mature ovum. No data were found in the literature as to the size of the mature ovum of the pig.
Of the fetal material secured, the litter at 15 mm. was the smallest which could be conveniently dissected and weighed. The
largest litter examined averages 262 mm. in crown-rump length,
and is not quite full term. However, the changes between this
stage and birth are probably slight, except in the matter of abso-
lute weight. That is, the relative size of the various organs would
probably not change much, since the changes are relatively slight
during the latter part of the fetal period.
For the data on the adult, a trip was made to the local (Columbia) packing house, and four hogs, probably about ten to twelve months old, were examined and weighed. The individual measurements so secured were averaged, and the averages used in constructing the various curves.
The method used for the fetal and adult material was that of weighing. The crown-rump length was also taken in all cases, as it forms another basis of comparison for the individuals and the different stages.
Each litter is considered as a unit. That is, the individuals
in each litter, or the three or four average pigs which were used
therefrom, were weighed individually and individual calculations made for the percentage which each organ forms of the whole.
Where the intestinal contents were determined (186 mm. and
above), their weight was subtracted from the gross body weight,
giving the net body weight, which was used in calculating the
percentages. The average of the percentages for each organ is
then taken for the litter, and this average is used in the table of
observations, the minimum and maximum percentages observed
in the litter being also indicated in parenthesis. In constructing
the various curves of relative growth, it was found convenient
to group together certain of the litters closely related in size, the
average of the litter averages being taken.
The following measurements were made on each pig: weight and crown-rump length were observed for the whole body ; the head, brain, eyeballs, spinal cord, thyroid gland, thymus gland,
right lung, left lung, heart, liver, stomach and intestines (with
mesentery and contents, also without contents where possible),
spleen, pancreas, suprarenal glands, gonads, kidneys and Wolffian
bodies, were each weighed separately.
The weights were taken carefully, the organs being placed in a
closed glass vessel of known weight. For the larger fetuses, the
organs were weighed to 0.001 g. (1 mg.), the body and head being
weighed to 0.1 g. For the smaller embryos (18 mm., 25 mm.,
37 mm., 41 mm.), the body and head were weighed to 0.001 g.,
and the organs (except those weighing more than 10 mg. in the
37 mm. and 41 mm. embryos) were weighed to . 0002 g. (0 . 2 mg.) .
For the 15 mm. embryos, the body and organs were weighed to
0.0001 g. (0.1 mg.).
The head was divided from the neck on a plane passing just behind the angle of the mandible and the cranium. Variations in this plane, which to a certain extent are unavoidable, lead to variations in the observed weight, and therefore in the relative size of the head.
The organs were weighed with contained blood, except the heart, which was opened and cleaned of the blood in the cavities. The brain and spinal cord were weighed with the pia mater but without the dura mater.
Since the age of the specimens is unknown, it is impossible to
construct accurate curves of growth either for the body as a whole
or for the various organs. However, by arranging the figures
representing the relative size (per cent of the net body weight)
according to the crown-rump length, curves can be drawn which
give an approximate idea of the changes in the relative growth
of the various organs during prenatal life. But no definite conclusions can be drawn from these curves as to the rapidity with
which these changes in relative size take place. The only exception to this is in the case of the body as a whole, where some data
by Keibel on the age of young pig embryos make it possible to
compare the growth in the early part with that in the remainder
of the prenatal and with the postnatal period.
A possible source of error lies in the fact that some of the litters
were preserved in formalin, while others were studied fresh. It
is well known that specimens preserved in formalin show an increase in total weight, amounting sometimes to 10 per cent or
15 per cent of the total. It is, however, improbable that this
increase will materially affect the relative size of the organs.
Observations
The observations have been condensed into a single table, from which curves expressing the relative growth have been made. A brief discussion of, and explanation for, the table and curves, follows.
Table 1 gives a summary of all the observations on the different litters used. In the first column will be found the serial number of the litter used. In the second column, the manner of preservation. . 'Form' indicates a 5 per cent aqueous solution of formalin. The length of time preserved is also indicated. In the third column is given the number of each sex of the individuals used (M-male; F-female).
In the fourth column is given the average crown-rump length,
in millimeters, for the litter, the minimum and maximum lengths
being given in parenthesis. Similarly in the fifth column is given
the average gross body weight for the litter in grams, together
with the minimum and maximum. The net body weight is also
given for the later stages, in which the intestinal contents could
be measured and subtracted.
The sixth column shows the average percentage by weight
which the head forms of the entire (net) body weight in each of
the various litters. The minimum and maximum percentage
found in the litter is given in parenthesis. Similarly in the succeeding columns is given the average percentage of the entire
(net) body weight (also minimum and maximum percentage) in
each litter for the brain, eyeballs, spinal cord, thyroid gland,
thymus, lungs, heart, liver, stomach and intestines with contents,
stomach and intestines empty, spleen, pancreas, suprarenal
glands, gonads, kidneys and (for the earlier stages) the Wolffian
bodies. In the last column is given the average percentage for
all the viscera added together, including the brain and spinal cord.
Figures for all the viscera were secured by adding up the average
percentages for the litter for each of the organs. The ovaries
and testes were averaged together, and the resulting figures added.
The weight of the stomach and intestinal contents is excluded.
Table 1
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Cite this page: Hill, M.A. (2024, May 5) Embryology Paper - Prenatal growth of the pig. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Prenatal_growth_of_the_pig
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
